This invention relates to the field of image recordation and playback, and in particular concerns user programming of control commands and data referring to recorded image tracks.
Current image recording formats for consumer equipment and the like utilize a high proportion of the available recording media for program content, namely video and audio. There is often little recording capability available for occasional use, such as to record user derived commands and data. One low data rate signal that can be recorded on a tape or similar medium is a timing indication signal. In the VHS tape format, control track pulses are generated at the image picture rate and are recorded together with the program content. On replay, these pulses are utilized to control reproduction so as to maintain the same rate as when recorded.
The control track pulses are recorded along an edge of the tape and mark each frame, whereas the video program content is recorded across the width of the tape. Typically in the NTSC TV standard the control track pulses have a repetition period of about 16.6 milliseconds and a duration or duty cycle of about 50%, that is, alternately 8 milliseconds at one level (e.g., high) and 8 milliseconds at another level (e.g., zero). In PAL operation the repetition period is 20 milliseconds and the pulse duration is about 10 milliseconds.
It has been recognized that such a control track signal does not make good use of the magnetic media. The part of the recorded control track signal that is needed to control timing of playback to match the image picture rate, is only a single edge such as the leading rising edge during each period. The remainder of the control track between the rising edges of successive periods could be varied to encode additional data.
In the early 1980's the Video Index Search Signal (VISS) was introduced and utilized an existing recording track for supplementary data such as a count for referencing particular portions of the program on the tape. The rising edges of the control track signal are used for playback speed control as above. According to the VISS standard, the trailing, non-time critical edge of the control track pulse can be controllably phase shifted, while maintaining the timing of the leading edge for use in controlling playback speed. Data is encoded by varying the phase of the trailing edge of the recorded command track signal between two distinct phases, representing digital true and false or one and zero value data bits.
This phase encoding method is uncomplicated. A logical "1" value can be encoded, for example, by advancing the phase of the trailing edge, thus shortening the positive portion of the control pulse to a duration of about 27.5% of the pulse repetition period. A logical "0" value delays the trailing edge as compared to a nominal 50% duty cycle, for example to produce a pulse of 60% duration. Simple timing and gating circuits can distinguish between pulses having a duty cycle that is longer or shorter than a reference duration (e.g., 50%), to decode the data into a serial digital data stream using this relatively dependable and inexpensive communication channel technique. However, each control track pulse period can encode only one data bit to a one or zero value. The data rate is slow.
Video cassette recorders (VCRs) can employ the VISS method to mark the starting point of a recording or a segment of a recording, as a means to enable cuing for subsequent replay. A standard for such index signals employs a marker sequence consisting of a 63 bit succession in which the first and last bits are logical zeros and all the intermediate bits are logical ones, the zeros and ones being distinguished by the phase difference of the trailing edge of the control pulse.
A similar use of control track encoding is employed by a system known as VHS Address Search Signal or VASS, which also uses phase difference of the trailing edge to encode logical data. The VASS system enables a digital address to be written to the control track during recording. The VASS signal may be used as an elapsed time indicator or to provide specific segment addressing for editing or control purposes. The standard VASS format contains an 11 bit header, similar to the header in VISS, with logical ones bounded by single zeros. The header is followed by a 16 bit data section that is typically used to store a four digit segment address. The segment address written onto the tape by phase variation of the command track pulse, is incremented by one for each new VASS address code. At the start of a new recording operation, the counter is reset. The VASS address codes can be written redundantly to ensure that they are decoded correctly, for example being written four times and requiring at least two successful decodes to be considered valid.
Similar data encoding/decoding techniques can be used to record information other than segment numbers or timing codes. U.S. Pat. No. 5,333,091 teaches an automated commercial break detector known as Commercial Free or Commercial Advance, whose purpose is to mark commercials so they can be automatically passed, blanked or played at fast-forward under control of a decoder responsive to the command track codes. The video and audio signals are analyzed for certain attributes during recording for identifying each commercial based on algorithms applied to audio and video parameters. Features are detected such as blank frames, advertising blocks, logos and the like, which are likely to be found in commercial messages, or which often precede or follow commercial messages. A fast-forward wind command is placed in the command track at the beginning of detected commercials, and a resume play command is recorded at the end.
The recorded commands need to slightly precede the beginning and end of the commercial break for completely passing over the unwanted commercial message. The video signal is analyzed for likely commercial breaks when recorded together with the timing signal on the command track. Then in a second pass, both the beginning and ending control commands are encoded or marked by overwriting the trailing edge of the existing command track signal. During subsequent user playback, upon detection of the fast-forward wind mark the video recorder is switched into a wind or fast-forward scan mode of operation. Detection of a resume-play pulse terminates the wind mode and resumes the play mode. Thus commercial advertising blocks are skipped over and only the wanted program material is replayed.
Detection of commercial advertising breaks during a television program can be difficult to accomplish accurately. Although many commercial breaks conform to a typical format or sequence of parameters, for example having one or more black frames between the program and the commercial break, some commercial breaks for one reason or another do not conform. A VCR having the capability of marking commercial breaks may, for example, accurately identify commercial breaks about 80% of the time.
An automated detection algorithm may fail to identify variant commercials with the result that the start of a commercial break is missed. When later viewing the tape, the user is required to view the unwanted commercial message. The opposite problem occurs when wanted program content happens to contain aspects of format that resemble a commercial break, and consequently satisfy the automated detection algorithm. In that case, a portion of the program content may be identified erroneously as a commercial break with and marked with wind and play marks encoded on the control track. Wanted program content then is skipped over when the tape is replayed, which is even more annoying than the presence of an occasional commercial. Should this occur, the user may wish to disable the commercial skipping feature entirely, so as not to miss wanted content.
Assuming that commercial breaks are identified with 100% accuracy and marked for commercial suppression, the user nevertheless may wish to view certain commercial breaks. It would be advantageous if this could be done without disabling the commercial break suppression feature entirely, and without the need for multiple remote control operations so that the suppression of commercials can be suspended for particular commercials only.
Commercial Advance concerns removing or skipping over part of the programming. Methods also are known for repeatedly playing back a recorded program or segment of a program between marked spots. For example, an announcement, advertisement or demonstration may be duplicated throughout the duration of a magnetic recording tape. When the tape end is reached and detected, the image replay equipment automatically rewinds to the start of the tape and recommences play back. This automatic repeat method may involve editing and duplicating the replay material repetitively along the tape, which may prove challenging for the occasional or non-professional user. A longer program simply may play from beginning to end and then repeat repetitively until manually stopped.
Repeated image replay can be accomplished by switching the VCR between a play mode and a rewind mode upon sensing an end mark or beginning and end marks on the tape, such as particular codes, a reflective marker, etc. Tape time or footage counter settings maintained by the VCR can also be used for this purpose. For example, at the start of a segment to be replayed, a tape counter is reset to zero. At the end of the replay material, rewind is selected and the counter (or timer) reading is stored automatically. The rewind continues until the count is zero, and play is selected. When the count reaches the stored count, rewind is selected again, enabling successive replays. Alternatively the tape length may be matched to that of the replayed message using an end-of-tape marker causing the tape to be rewound to the start or to an earlier marker at which the play mode is automatically selected and the material is replayed again.
Beginning and end markers are resident on the tape, whereas tape counter techniques operate from information stored in the replay device or generated by the replay device. Methods relying on storage in the replay device have the limitation that changes in tape counter setting, for example occurring with removal of the tape from the replay device, defeat the automation. Markers resident on the tape are independent of this limitation but have the limitation that the beginning and end markers are relatively permanent and immovable indicia.
U.S. Pat. No. 4,549,231 to Namiki shows an arrangement in which a control track is coded for fast forward and then play in order to skip unwanted portions of the video program.
European Publication 0526739A1 of Hitachi, indicates the desirability of encoding various commands along with the recorded video signal.
A simple method and apparatus are needed which allow a user manually to program a sequence of reproduced images and to store, for example on the tape, suitable control commands to facilitate future automated reproduction of the image sequence.